1. Field of the Invention
This invention relates to a control system for a small electric vehicle or car usable as an electric wheelchair, golf cart or the like.
2. Description of the Related Art
Small electric vehicles of the type referred to above are taught by U.S. Pat. No. 4,729,447 and Japanese Laid-Open Patent Application No. Hei 10(1999)-165454. In addition, Japanese Patent No. 2,724,565 teaches control for preventing abrupt drive-off from standstill, enabling smooth drive-off, and, when the small electric vehicle rolls back owing to insufficient torque during hill climbing or the like, increasing the output torque of the electric motor for driving the small electric vehicle to enable smooth hill climbing.
The power trains of vehicles of this type ordinarily constituted of a combination of an electric motor and a reduction gear mechanism, and the electric motor output is transmitted to the wheels through the reduction gear mechanism. When the small electric vehicle is driven off at a situation where the amount of reduction gear mechanism backlash is great, therefore, a shock is imparted to the operator/passenger (s). The shock is particularly pronounced when the vehicle is equipped with a large-capacity electric motor to enhance hill-climbing performance.
However, the prior art has focused solely on smooth drive-off control and the like and provides no measure whatsoever regarding the shock produced by reduction gear mechanism backlash.
Moreover, Japanese Laid-Open Patent Application No. Hei 5(1993)-30612 teaches utilizing the electric motor as a regeneration brake during deceleration, for example, to achieve smooth driving, when alternate acceleration and deceleration are repeated.
This type of vehicle is equipped with, for example, a maximum speed switch for inputting a maximum speed and an accelerator (accelerator lever) for inputting drive-off and stop instructions, and a command speed is calculated and used to increase/decrease the driving speed to obtain a set speed (desired speed) calculated based on the outputs of the maximum speed switch and the accelerator. Since the rate of speed increase/decrease (acceleration or deceleration) is constant, however, the vehicle driving speed changes abruptly in response to a slight manipulation of the accelerator by the operator. This gives the operator an unnatural feeling.
In other words, this prior art (mentioned in 5(1993)-30612) technology has a problem regarding the driving xe2x80x9cfeelxe2x80x9d but none of the conventional technologies provide any countermeasure regarding this point whatsoever.
An object of this invention is therefore to provide a control system for a small electric vehicle overcoming the foregoing problem that enables smooth drive-off while also reducing or eliminating drive-off shock caused by reduction gear mechanism backlash even when a high-capacity electric motor is installed to enhance hill-climbing performance.
Another object of this invention is therefore to provide a control system for a small electric vehicle overcoming the foregoing problem that improves the feel of driving by avoiding abrupt change in driving speed even when the operator manipulates the accelerator slightly.
For achieving the first object, there is provided a system for controlling a small electric motor vehicle equipped with an electric motor for driving wheels through a reduction gear mechanism, comprising: a speed setting switch which generates a signal indicative of a maximum speed inputted by a vehicle operator; an accelerator which generates signals indicative of drive-off instruction and stop instruction inputted by the vehicle operator; and an electric motor controller which inputs the signal generated by the speed setting switch and the accelerator and determines a desired speed and conducts a first voltage control of the electric motor such that a driving speed converges the desired speed; wherein the electric motor controller conducts a second voltage control to immediately apply a first predetermined voltage to the electric motor when the drive-off instruction is generated from vehicle standstill and then to increase the voltage at a predetermined rate until the voltage exceeds a second predetermined voltage, and then conducts the first voltage control such that the driving speed converges to the desired speed.
For achieving the second object, there is provided a system for controlling a small electric motor vehicle equipped with an electric motor for driving wheels through a reduction gear mechanism, comprising: a speed setting switch which generates a signal indicative of a maximum speed inputted by a vehicle operator; an accelerator which generates signals indicative of drive-off instruction and stop instruction inputted by the vehicle operator; a speed controller which calculates a set speed based on the signals of the speed setting switch and the accelerator and calculates a command speed to accelerate or decelerate a driving speed at a rate which is varied all with a difference between the set speed and the command speed, such that a driving speed converges to the set speed; and an electric motor controller which feedback-controls a voltage to be applied to the electric motor such that an error between the command speed and the driving speed decreases.